The problem. A company's invoices and its signed contracts had quietly drifted apart across a year. The billing system was configured correctly, so nothing looked broken, but individual invoices were going out wrong.

What I did. Checked 33 issued invoices line by line against contracted terms, recalculating pro-rations from actual day counts, verifying price-change timing against effective dates in each contract, and checking whether percentage-based charges had been calculated on the basis the agreement actually defines.

What it found. Ten discrepancies worth a net 2,430 recoverable. Eight of them were revenue never collected: a quarter that was never invoiced at all, an 8% escalation clause nobody had applied for three months, an onboarding fee that had no recurring trigger, and 4,240 bookings of overage above a contractual cap that was never being monitored.

Where this usually goes wrong. The most expensive error in this kind of work is never arithmetic. It is definitional. A commission calculated on gross transaction volume when the agreement defines it on net revenue produces a perfectly correct sum from the wrong number. Automated checks never catch that. Only reading the agreement against the invoice does.

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